Canine infectious respiratory disease (CIRD) is a highly contagious disease common in dogs housed in crowded conditions such as re-homing centres and boarding or training kennels. Many dogs suffer only from a mild cough and recover after a short time, however in some cases a severe bronchopneumonia can develop (Appel and Binn, 1987).
The pathogenesis of CIRD is considered to be multifactorial, involving several viruses and bacteria. The infectious agents considered to be the major causative pathogens of CIRD are canine parainfluenzavirus (CPIV) (Binn et al., 1967), canine adenovirus type 2 (CAV-2) (Ditchfield et al., 1962) and the bacterium Bordetella bronchiseptica (Bemis et al., 1977, Keil et al., 1998). Also, canine herpesvirus, human reovirus and mycoplasma species have been isolated from dogs with symptoms of CIRD (Karpas et al., 1968, Lou and Wenner 1963, Randolph et al., 1993) Additional factors like stress may also be important.
CIRD is rarely fatal but it delays re-homing of dogs at rescue centres and it causes disruption of schedules in training kennels as well as considerable treatment costs.
Vaccines are available against some of the infectious agents associated with this disease, namely Bordetella bronchiseptica as well as CPIV and CAV-2. However, despite the use of these vaccines, CIRD is still prevalent in kennels world-wide, which is possibly due to the vaccines not providing protection against all the infectious agents involved in CIRD.
We have discovered a novel coronavirus, which we have called canine respiratory coronavirus (CRCV), in a large kenneled dog population with a history of endemic respiratory disease, and we have shown that this virus is associated with CIRD.
Some members of the family coronaviridae are known to cause respiratory disease in humans, cattle, swine and poultry (Mäkelä et al., 1998, Pensaert et al., 1986, Ignjatovic and Sapats 2000). For example, bovine respiratory coronavirus is associated with shipping fever in cattle which is a multifactorial respiratory disease (Storz et al., 2000).
However, coronaviruses were not suspected to have a role in the pathogenesis of CIRD. Indeed, with only a single exception, canine coronaviruses have been reported to be enteric viruses and to cause acute diarrhoea mainly in young dogs (for example, Tennant et al., 1993). In a large study of viruses involved in canine respiratory diseases, Binn et al. (1979) reported the detection of a canine coronavirus in the lung of a single dog that was also infected with SV5 and canine adenovirus 2, two other viruses that are associated with canine respiratory disease.
There are 30-40 dog vaccines commercially available in the UK for use against a number of pathogens that can cause a range of diseases, such as neurological, enteric, hepatic and respiratory diseases. Most of these vaccines contain microbial agents such as Distemper virus, Canine Adenovirus-2, Canine parvovirus, canine parainfluenza virus and Leptospira canicola and L. icterohaemorrhagiae. None of these vaccines contain canine coronaviruses.
The dog vaccines for use against canine respiratory diseases are marketed as vaccines for “kennel-cough” (see below). All of the vaccines contain Bordetella bronchisepticum, which is a bacterium associated with “kennel cough”.
Coyne M. J. & May S. W., (1995) in their article entitled “Considerations in using a canine coronavirus vaccine” (published as a Pfizer Technical Bulletin on the Internet at http://www.pfizer.com/ah/vet/tref/trbull/ccv.html), lists over 20 commercially available vaccines against either canine coronaviruses alone or against canine coronaviruses together with other organisms. Each of these vaccines is for canine enteric disease, and there is no suggestion that a canine coronavirus may be associated with respiratory disease.
U.S. Pat. Nos. 6,057,436 and 6,372,224, both to Miller et al and assigned to Pfizer, Inc., describe the spike gene of the enteric canine coronavirus and uses therefor, including its use as a vaccine against gastroenteritis. Neither of these two patents suggest that a canine coronavirus may be involved in CIRD.
Members of the family coronaviridae are enveloped viruses, 80-160 nm in diameter, containing a linear positive-stranded RNA genome. The structural proteins of coronaviruses are the spike glycoprotein (S), the membrane glycoprotein (M) and the nucleocapsid protein (N). The hemagglutinin/esterase glycoprotein (HE) is found only on the surface of group II coronaviruses (e.g. bovine coronavirus and murine hepatitis virus) (Spaan et al, 1988). Further details of the structure of coronoviruses may be found in the chapter by Cavanagh et al entitled “Coronviridae” p 407-411, in “Virus Taxonomy, 6th Report of the International Committee on Taxonomy of Viruses”, pub. Springer-Verlag Wein, New York, Eds. Murphy et al, which is incorporated herein by reference.